Silencing of foreign DNA in bacteria

Xenogeneic silencing proteins facilitate horizontal gene transfer by silencing expression of AT-rich sequences. By virtue of their activity these proteins serve as master regulators of a variety of important functions including motility, drug resistance, and virulence. Three families of silencers have been identified to date: the H-NS like proteins of Gram-negative bacteria, the MvaT like proteins of Pseudomonacae, and the Lsr2 proteins of Actinobacteria. Structural and biochemical characterization of these proteins have revealed that they share surprising commonalities in mechanism and function despite extensive divergence in both sequence and structure. Here we discuss the mechanisms that underlie the ability of these proteins to selectively target AT-rich DNA and the contradictory data regarding the mode by which H-NS forms nucleoprotein complexes.

► Many bacteria contain xenogeneic silencing proteins that silence AT-rich DNA.
► There are three structurally distinct families of xenogeneic silencers.
► Lsr2 of Mycobacteria and H-NS of enterobacteria bind DNA by a similar mechanism.
► Xenogeneic silencers form higher order structures on DNA through cooperative interactions.
► Two modes of binding by H-NS have been proposed, bridging and stiffening.